The present invention relates to soil decontamination, particularly to the use of electrical heating technology for removing volatile organic compounds from soils, and more particularly to electrode well for powerline-frequency electrical heating of soils used in combination with vacuum extraction to remove organic compounds from contaminated soils.
Cleanup of soil contamination by volatile organic compounds, either on the ground surface or subsurface, such as gasoline and trichloroethylene (TCE) has become a major concern, especially where the contaminated areas are located adjacent to underground water. Various prior approaches have been utilized to eliminate the soil contamination, often caused by leakage of fuel or oil tanks, industrial wastes, fuel or oil spills, etc. The primary prior approach to remove contamination from the soil has been excavation to physically remove the contaminated soil. However, the removed soil remains contaminated thus posing a storage problem, as well as the costs of removal and hauling. Also, excavation can only be carried to a certain depth, leaving contamination beyond that depth. Thus, there has been a need for cost effective, rapid cleanup of localized underground contamination.
The present invention provides a partial solution to surface or underground soil decontamination, particularly where the contamination is located less than about fifty feet beneath the ground surface. The invention involves one or more electrode wells for powerline-frequency electrical heating of the contaminated soil in combination with an extraction well or wells under subatmospheric conditions. Heating of the soil by the electrode wells enables the volatile organic compounds, such as gasoline and TCE, to be withdrawn via the extraction well for treatment, storage, and disposal above the ground surface. The electrode wells and the extraction well may be located in small holes drilled by augers or small drill rigs, thus reducing the costs of insertion of the wells. The electrode wells utilize one or more electrodes surrounded by a conductive backfill material, such as damp sand, steel shot, or graphite to increase conductance into the soil formation. A preferred embodiment utilizes mild steel pipe as the current-carrying conductor.